1. Field of the Invention
The present invention relates to a composition for permanent hair waving based on straight-chain N--C.sub.3 --to N--C.sub.3 -C.sub.6 -alkyl- or N--C.sub.3 -C.sub.6 -hydroxyalkyl-substituted mercaptoacetamides, as the keratin-reducing ingredient, and to a method for permanent hair waving using this composition.
2. Prior Art
The classic technique for permanent hair waving is familiarly based on two treatment steps: In the first step, the cystine-disulfide bridges of the keratin of the hair are opened by the action of an agent that contains a reducing ingredient (waving composition). The hair is then put into the desired form. In a second step, cystine-disulfide bonds are closed again using a fixative, that is, an agent containing an oxidant ingredient.
As the pioneering work in German patents 948 186 and 972 424 demonstrate, thioglycolic acid, for instance in the form of an ammonium or monoethanolamine salt, is used as a classic permanent hair waving reducing agent. Other typical reducing agents are 2-mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, cysteine, and derivatives of these compounds, as well as certain mercaptocarboxylic acid esters.
Alkaline-adjusted preparations based on mercaptocarboxylic acid esters, despite being adequately effective, cause hair damage, which is expressed for instance in increased hair breakage. Often, these compositions also undesirably stress the scalp. Finally, the unpleasant odor of the reducing agents used requires intensive perfuming of the products. By using 2-mercaptopropionic acid, it is possible to solve some of these problems. However, in comparison to thioglycolic acid, which is widely used, thiolactic acid produces weaker waves.
For gentle, permanent waving of damaged and especially bleached or dyed hair, waving compositions that are adjusted to be slightly acidic to neutral are preferably used. From a professional standpoint, over the last 35 years, the thioglycolic acid esters have proved to be the reducing agents best suited for this purpose.
A major disadvantage of acidic hair waving compositions based on thioglycolic acid esters, however, is that they are poorly tolerated by the eyes and skin, and the sensitizing effect of the thioglycolic acid esters, so that the use of these hair waving compositions is widely avoided at present. Instead of the mercaptocarboxylic acid esters, mercaptoacetamides such as thioglycolic acid amide or alkyl- or hydroxyalkyl-substituted amides have also been used. Such compounds are known from German Patent DE-C1 144 440 and European Patent EP-A 0 455 457. Like the mercaptocarboxylic acid esters, these substances have a high waving potential at low pH values, but in terms of toxicology they are even more critical than the mercaptocarboxylic acid esters.